I own a USB powered Sound BlasterX G6. Audio output works with no problems at all under the latest LTS. However, I cannot get the mic input to work. I have tried various things after searching for answers to this, but I have had no success. I have a Logitech BRIO webcam connected, and Ubuntu is using its mic for input by default. The Logitech webcam mic does work, but I cannot show my Sound Blaster G6's mic to show in settings or function using alsamixer. Here is how Settings appear for me currently:

When I choose Microphone - Logitech BRIO, I do hear input. I get a lot of noise using the webcam's mic, because it is right next to my workstation. I have a headset plugged into my Sound Blaster G6, but I cannot get the external mic to work. When I use alsamixer to select Sound Blaster G6 and External mic, I lose all audio from the Sound Blaster completely. I can only recover audio by restarting alsa and/or rebooting.
Any suggestions to resolve this issue? The Logitech BRIO mic is the only functional mic in my system. Perhaps there is an issue with systems having more than one mic?